They’re both good, but overall I’d recommend Zinn. The Park book is a bit prescriptive (“use a Park G13 tool to torque to 17.4Nm….”) whereas Zinn is a bit more practical (“In your workshop, do it like this… if you’re out on the trail and you’re stuck, you could try hitting it with a rock like this…”). Pretty sure he even has peeing on a frozen freehub in there…